Solar cells are devices that convert the energy of light into electricity using the photovoltaic effect. Solar power is an attractive green energy source because it is sustainable and produces only non-polluting by-products. Accordingly, a great deal of research is currently being devoted to developing solar cells with enhanced efficiency while continuously lowering material and manufacturing costs.
When light hits a solar cell, a fraction of the incident light is reflected by the surface and the remainder transmitted into the solar cell. The transmitted light/photons are absorbed by the solar cell, which is usually made of a semiconducting material, such as silicon. The absorbed photon energy excites electrons from the atoms of the semiconducting material, generating electron-hole pairs. These electron-hole pairs are then separated by p-n junctions and collected by conductive electrodes that are applied on the solar cell surface. These conductive electrodes typically comprise an electroconductive paste composition.
Traditional electroconductive pastes contain metallic particles, glass frit, and an organic vehicle. These components are usually selected to take full advantage of the theoretical potential of the resulting solar cell. The metallic particles act as the conductive component of the surface electrode. The organic vehicle provides the medium through which all of the components are combined. The glass frit component has a number of purposes, one of which is to improve contact between the electrode and the underlying silicon surface. It is desirable to maximize the contact between the electroconductive paste and silicon surface, as well as with the metallic particles themselves, so that the charge carriers can flow through the interface and then through the surface electrodes. The glass particles in the electroconductive paste provide the media by which the paste builds contact between the metal and the underlying silicon substrate. The glass component must have specific properties in order to achieve optimal contact. Thus, the goal is to minimize contact resistance while improving solar cell efficiency. Known glass compositions have high contact resistance due to the insulating effect of the glass in the interface of the electrode and silicon wafer. Further, glass frit is known to have wide melting temperature ranges, making their behavior strongly dependent on the processing parameters. Accordingly, electroconductive paste compositions with improved electrical properties are desirable. Specifically, electroconductive paste compositions with improved glass frit components are needed.